Crown institute Agresearch is releasing more Irish wasps in the South Island to combat a weevil that is eating clover pastures.
AgResearch scientists say there are potentially damaging populations of the weevil spreading from Greymouth north to Karamea on the West Coast.
Dr Scott Hardwick says the Irish wasp, a natural predator of the pest, is present at many of the same locations of the weevil, but the weevil outnumbers the wasp further south on the West Coast.
He says AgResearch is now releasing the wasp south of Greymouth.